No one is calling you little brother. Or more importantly, no one is calling Portland Seattle's little brother. It's the way of thinking by some (just some) that is little brotherish. When I lived in Seattle I never heard any hate for Portland. There was some UO hate (I was at UW), but even then it was nothing like what I hear going the other way. It seems like anytime Seattle is brought up in conversations (both here and just in general in Portland), there is always a vocal minority trying to one up Seattle. Have you been to Vivace? Oh, Stumptown is better! The winters in Portland suck! But it's so much worse in Seattle! (I have heard this numerous times).
Like I said, I personally like Portland more, but I can see that in some (you may or may not actually fit, but your statements seems to lump you in) just can't accept any favorable mention of Seattle without interjecting something about Portland being better.
About your "Seattle fans" generalization, can a WSU fan root for the Seahawks/M's/Sounders? They are part of the Seattle fan base that WSU fans must hate since it includes those hated Huskies.